1. Field of the Invention
This invention relates to hydraulic lifters used in valve trains of internal combustion engines and more particularly to a self-contained hydraulic lifter in which the fluid is sealed within the assembly with no provision for its replenishment from any external source during operation.
2. Prior Art of the Invention
The conventional self-contained hydraulic lifter of this type includes a hollow cylindrical plunger which slidably fitted (or disposed or mounted) in a cylindrical body, and a diaphragm that isolates the reservoir in said plunger from atmospheric air is press-fitted to be fixed to the upper opening's inner periphery of said plunger. The cylindrical upper rim of the diaphragm is simply press-fitted to be fixed to the inner periphery of the opening on top of said plunger. Consequently, there is a fear of said diaphragm being floated to deteriorate the sealing performance and causing oil leakage because of the thermal effects after it is press-fitted and the vibration of the running engine transmitted through the push rod, push rod seat, etc.
A metal ring is sometimes embedded in the upper circumferential portion of the diaphragm to improve the sealability of the diaphragm, but the metal ring used for the conventional diaphragm is simply a cylindrical one. As a result, when the engine runs at a high speed, a great force is applied to the fixed portion of the diaphragm with increase in the acceleration of the engine valve train, so that the fixed portion of said diaphragm, being unable to withstand that force, moves downward causing a fear of the diaphragm contacting the inner bottom of the plunger. Further, as the outer periphery surface of the metal ring (29) is simply a flat cylindrical surface, the contact between the metal ring embedded portion and the diaphragm become loose, causing a fear of the diaphragm alone moving downward.
One possible means of not allowing the diaphragm contacting the bottom in the plunger when the diaphragm has moved downward is to increase the gap between the diaphragm and plunger bottom or to increase the clamping margin of the diaphragm fixed portion (press-fitted portion). In the former case, however, the ability to absorb the change in the volume of the oil deteriorates if the diaphragm is shortened, leading to damage of the diaphragm. On the other hand, if the plunger is extended so as not to allow the diaphragm to contact the plunger inner bottom, it will increase the weight and the overall length of the lifter and eventually increase the acceleration of the valve motion system. If the clamping margin is increased, problems such as torn rubber of the fixed portion arise.